用Java克隆子类

我需要在 Java中克隆一个子类,但是在代码发生这种情况时,我不会知道子类类型,只知道超类.这样做的最佳设计模式是什么？

例：

class Foo {
    String myFoo;
    public Foo(){}
    public Foo(Foo old) {
        this.myFoo = old.myFoo;
    }
}

class Bar extends Foo {
    String myBar;
    public Bar(){}
    public Bar(Bar old) {
        super(old); // copies myFoo
        this.myBar = old.myBar;
    }
}

class copier {
    Foo foo;

    public Foo makecopy(Foo oldFoo) {

        // this doesn't work if oldFoo is actually an
        // instance of Bar,because myBar is not copied
        Foo newFoo = new Foo(oldFoo);
        return newFoo;

        // unfortunately,I can't predict what oldFoo's the actual class
        // is,so I can't go:
        // if (oldFoo instanceof Bar) { // copy Bar here }
    }
}

解决方法

如果您可以控制要复制的类,那么虚拟方法就是前进的方法：

class Foo {
    ...
    public Foo copy() {
        return new Foo(this);
    }
}
class Bar extends Foo {
    ...
    @Override public Bar copy() {
        return new Bar(this);
    }
}

(理想情况下,使类成为抽象或有效的最终.)